1. Field of the Invention
The present invention relates to a technique of providing information to mobile clients.
2. Description of the Related Art
Some systems have been proposed to provide preset announcement information (for example, advertisement information, public information, or guide information) when a client, which is a mobile device like a PDA (portable digital assistant), a portable terminal, an electronic organizer, or a wearable computer, approaches a predetermined location (for example, a store, an automatic vending machine, a mobile shop, a facility, a condominium, an apartment house, or a booth in some event). In such a system, the client utilizes a GPS (global positioning system) or another adequate system to acquire positional information representing the own position and transmits the positional information to a base station. The base station then gives the announcement information to the client.
The technique of providing information to mobile devices by utilizing GPS is disclosed in PATENT LAID-OPEN GAZETTE No. 2002-259253.
The mobile device like the PDA, the portable terminal, the electronic organizer, or the wearable computer has a restricted battery capacity. It is accordingly difficult to build a GPS or equivalent system having large power consumption in the mobile device. The mobile device of high portability also has only a limited space in the casing. Incorporation of the GPS or equivalent system in the limited space is against the requirements of size and weight reduction of the mobile device. It has thus been not practical that the mobile device has the detection function of positional information and the position specification function based on the positional information.